As well as having one of the spaciest names to exist, NASA’s OSIRIS-REx mission has a groundbreaking aim – to bring back a sample of asteroid Bennu to Earth. Instruments onboard the orbiting spacecraft have been helping scientists to identify the best position to collect this sample from. Last fall, one of these instruments, the shoe-box-sized Regolith X-Ray Imaging Spectrometer (REXIS), made an unexpected detection off the limb of Bennu: a newly flaring black hole, 30,000 light-years away.
Designed to measure the X-rays that Bennu emits in response to incoming solar radiation, REXIS is a collaborative venture by students and researchers from MIT and Harvard. During the spacecraft’s observations of the space around Bennu on Nov 11, 2019, the team noticed an X-ray source, which had not previously been cataloged.
This source turned out to be a newly flaring black hole pulling in matter from an orbiting star. As the matter spirals into the spinning disk around the black hole, a huge amount of energy is released, primarily in the form of powerful X-ray bursts. Almost as if the black hole were “singing in the language of X-rays,” as NASA once described it.
“Detecting this X-ray burst is a proud moment for the REXIS team. It means our instrument is performing as expected and to the level required of NASA science instruments,” Madeline Lambert, an MIT graduate student who designed the instrument’s command sequences that serendipitously revealed the black hole, said in a statement.
X-rays are shielded from the Earth by our atmosphere, therefore measurements of bursts such as this one can only be observed in space. In fact, this black hole was first detected only a week earlier, by Japan’s MAXI telescope, hence the object’s designated name, MAXI J0637-430. NASA’s NICER telescope also confirmed this discovery just a few days later.
Whilst both of these telescopes are onboard the International Space Station (ISS) in low-Earth orbit, REXIS, on the other hand, was millions of miles away from Earth, orbiting its asteroid. Therefore the X-ray burst from the 30,000 light-years-away black hole was the “first such outburst ever detected from interplanetary space.”
REXIS will continue to be used as a preparation tool for the next generation of scientists, engineers, and project managers in the development and operations of spaceflight hardware. Having had nearly 100 students pass through the REXIS team since it began, the teachers believe this surprise detection may have been one of the most valuable experiences thus far.
“We set out to train students how to build and operate space instruments,” MIT professor Richard Binzel, instrument scientist for the REXIS student experiment, said. “It turns out, the greatest lesson is to always be open to discovering the unexpected.”